With the continuing rise in popularity of light trucks and cargo vans, there exists a need to provide tires that have the ability to be driven on paved roads while carrying heavy loads without excessive noise yet also to be capable of being driven in heavy snow or wet roads. Often these tires will be driven in flooded or wet roadway conditions. As an added condition, these multipurpose traction demands for the tire must be coupled with excellent tread wear.
Historically, tires have been able to meet one or two of the above-referenced design requirements but usually at the sacrifice of the other design features.
Snow tires for cargo van tires would achieve good traction usually by opening the tread pattern and providing large block type tread elements. These tires generally were very noisy and had poor treadwear when driven at highway speeds on paved roads.
A latter developed asymmetric nondirectional tire was developed for the light truck and sport utility vehicles called the Wrangler GSA. This tire employed a unique triple traction feature that provides excellent uniform wear across the tread pattern regardless of the wheel position. The tire has good noise and more than adequate traction in a variety of conditions such as snow, off road, and on road wet or dry. The tread pattern disclosed in U.S. Pat. No. 5,415,215 was one of the first truly multipurpose tires for these types of vehicles. The Wrangler GSA tire has been commercially very successful.
From that tire, a superior wet traction tire was developed employing two wide aquachannels in combination with the triple traction feature. The tire has been entitled the Wrangler Aquatred and it is disclosed in U.S. patent application Ser. No. 08/228,056. This tire demonstrated that deep water traction could be enhanced without sacrificing the wear and other performance features of the original Wrangler GSA tire.
The Wrangler Aquatred demonstrated that while the all around performance of these light truck and sport utility tires must be very good, some drivers still have special needs or concerns requiring the more specialized type tire performance in one or more feature.
A particular specialized problem arises in the application wherein heavily loaded cargo trucks such as the light truck or cargo van size vehicles are concerned. These vehicles are primarily driven on paved roads. The commercial nature of this vehicle demands that the tires exhibit excellent treadwear and very low tire noise. The commonly accepted tread for such a vehicle has generally been a ribbed-type tread. The ribs are generally circumferentially continuous bands of rubber. The use of lateral grooves is limited primarily-because lateral grooves accelerate the rate of treadwear. This is due to the fact that voids such as grooves generally provide traction, but naturally a loss of treadwear results because the net-road contacting area is reduced by the use of grooves. A second contributing factor to the loss of treadwear is the lateral grooves create an entry and exit point into and out of the tires contact patch that can initiate heel/toe wear.
For these reasons, the tire designers prefer to employ ribs where possible. The other added benefit to ribs are they are inherently more quiet that tread block elements.
The dilemma is to devise a way to increase the traction performance of these treads without sacrificing treadwear or noise performance of rib-type treads. While the rib-type tread wears generally well, it has occurrences of irregular wear along the edges of the circumferentially continuous grooves. This irregular wear is most problematic when the ribs exhibit variable stiffness.
There has been a continual trade-off in attempting to increase the aggressive wet road and snow traction performance of these tires while maintaining the treadwear durability and noise constraints.
The invention disclosed in this patent application teaches a novel tread that is both quiet and long wearing while also achieving excellent road traction.